Typical vacuum fluorescent displays include in their structure a filament, a suspended acceleration grid, one or more anodes and one or more phosphors, all enclosed within a sealed package having a low pressure (a vacuum). The filament is heated, such as by an AC current, to a temperature at which it will emit electrons. A suspended acceleration grid biased at a potential higher than a bias of the filament accelerates electrons emitted from the filament toward an anode, also biased higher than the filament bias. On the anode, a phosphor is deposited and emits light in response to the bombardment of electrons emitted from the filament and accelerated by the grid and anode.
It is known to use this vacuum fluorescent display technology in active displays. Such active displays may use either thin film or bulk silicon transistor technology. In the active matrix display, each phosphor element comprises a pixel and is individually controlled by one or more transistors that are selectively addressed. An example system in which redundancy is used to increase display yield is shown in U.S. Pat. No. 5,151,632.
In active matrix displays where high brightness is desired, the filament is placed closer to the anode and phosphors. This lessens the room between the filament and the anode and phosphor for the suspended grid. Once the distance between the filament and anode reaches a certain size, it is no longer practical to suspend an acceleration grid between the filament and the anode and the display is used without the acceleration grid.
It is known that in order to obtain more uniform electron bombardment of the phosphor areas of a conventional vacuum fluorescent display, a wire mesh grid may be physically interposed between the filament and phosphor and biased generally at some intermediate voltage.
It is known that an appropriate alternate electron source of vacuum fluorescent displays is comprised of a class known as field emission sources. These compare to the conventional electron source that is a thermionic filament. Field emission sources include cold cathode emitters, field emission arrays, Spindt cathodes, and other non-thermal electron sources known to those skilled in the art. Electron sources, both thermal and field emission based, are referred to collectively herein by the term "filament."